Mechanisms of Methylene Blue Degradation by Nano-Sized β-MnO_2 Particles

摘要

Degradation of a dye by 1 -D nano-sized β-MnO_2 particles was investigated to understand the mechanisms involved. Batch experiments were performed in a system of β-MnO_2, hydrogen peroxide (H_2O_2), methylene blue (MB), and radical scavengers. The prepared β-MnO_2 had a 1-dimensional nano-sized structure and showed a negative zeta potential at pH higher than 3.7. In the presence of H_2O_2, MB was rapidly degraded by β-MnO_2. The rate of MB degradation was not significantly inhibited by the initial pH values from 6.05 to 10.02, but notably decreased at pH 3.04, at which point the β-MnO_2 particles dissolved. The effect mechanisms of operational parameters (i.e., H_2O_2, catalyst dose) in β-MnO_2/MB/H_2O_2 system were investigated. The removal rate of MB was remarkably reduced in the existence of p-quinone and was even more affected when sodium azide was added, indicating that the singlet oxygen radical (~1O_2) plays an important role. The obtained results point out that MB degradation by nano-sized β-MnO_2 is due to the catalytic oxidation of H_2O_2 on β-MnO_2 surface reactive sites, rather than surface oxidation or adsorption. The reusability of nano-sized β-MnO_2 was also examined after five times of recycling to evaluate the applicability of β-MnO_2 for wastewater treatment.